The present invention relates to a high speed continuous printing (decorating) machine for printing (decorating) cylindrical containers such as can bodies and, more specifically, relates to a printing machine having a mandrel wheel skip-print apparatus malfunction sensing and response assembly.
Can printing (decorating) machines, especially high speed continuous can printing machines, operate by the impingement of a rotating, image-carrying blanket wheel and an oppositely rotating can carrying mandrel wheel assembly. The blanket wheel comprises an endless blanket which is at least as wide as the length of the cans being printed. The blanket carries a series of web ink images circumferentially spaced on its resilient periphery. The mandrel wheel assembly comprises a mandrel wheel mounted with a series of circumferentially spaced, rotatable mandrels over which cans are fitted. The cans rotate on the mandrel wheel into registry and contact with the images on the surface of the blanket wheel. Each mandrel generally includes structure for removing cans from or drawing cans onto the mandrel.
During high speed can printing, a can will occasionally fail to properly seat on a mandrel or a gap will occur in the continuous can infeed to the machine causing one or more mandrels not to have a can received thereon. In such circumstances, it is necessary that the mandrel not be moved into contact with the blanket wheel to prevent the mandrel surface from being printed and contaminated. A number of different mechanisms have been utilized in the past to provide such a "skip-print" feature.
Hartmeister et al., U.S. Pat. No. 3,655,853 issued May 30, 1972, which is hereby specifically incorporated by reference for all that it contains, describes a continuous printer and skip-printer mechanism comprising a plurality of blanket holder segments on a rotated drum successively movable into and out of printing position, a stationary cam, a cam follower on each segment, and operative connections including a withdrawable bridge member between the cam follower and each blanket holder segment for moving the segment into printing position. An air cylinder responsive to a malfunction signal actuates a pivotally mounted trigger and connecting rod which are part of skip-print means for withdrawing the bridging member from the operative connections between the cam follower and each blanket holder segment, thereby producing a gap in the operative connections and preventing movement of the segment into printing position when malfunction occurs, without interrupting subsequent printing operations.
Zurick, U.S. Pat. No. 3,851,579 issued Dec. 3, 1974, which is hereby specifically incorporated by reference for all that it contains, describes a trip mechanism for a continuously rotating can printing or coating machine having rotatable can shaft supports, which is operable to displace the support from a print blanket. The trip mechanism includes an eccentric sleeve between the shaft and a bore which is rotatable with the bore and about the shaft. In a normal position, the sleeve holds the shaft in position to effect contact between a can mounted thereon and the print blanket. A detector provides a trip signal in response to the absence of a can. A trip cam and trip cam follower pair are provided, one of which is mounted on the eccentric sleeve. The trip cam is thrown from a normal print to a trip position in response to a trip signal. The trip pair is positioned to engage one another when the cam is in the trip position to cause rotation of the sleeve whereby the shaft and can support are displaced away from the print blanket.
Sirvet, U.S. Pat. No. 4,037,530 issued July 26, 1977, which is hereby specifically incorporated by reference for all that it contains, describes a pocket mandrel wheel having mandrels mounted on mandrel spindles that pivot to move the mandrels laterally to prevent the mandrels from contacting an associated printing wheel. The mandrel spindles are attached to the mandrel wheel by a pivot arm that controls the radius of the mandrel's line of motion as the mandrel wheel rotates. The pivot arm causes the mandrel spindle to rotate the mandrel in response to an electronic system that detects improperly seated cans on the mandrels. The pivot arm rests against an interposer block having a recessed step, and the mandrel is withdrawn when the block is moved in response to a signal from the electronic system so that the pivot arm rests against the recessed portion of the block. The movement of the block is controlled by a mechanical system that moves the pivot arm away from the block prior to the time when the mandrel may be tripped.
Other patents describing mandrel wheel operations, which are all hereby specifically incorporated by reference for all that is disclosed therein, include Cracho et al., U.S. Pat. No. 3,496,863 issued Feb. 24, 1970; McMillin et al., U.S. Pat. No. 4,138,941 issued Feb. 13, 1979; Skrypek et al., U.S. Pat. No. 4,140,053 issued Feb. 20, 1979; Stirbis, U.S. Pat. No. 4,267,771 issued May 19, 1981; Stirbis, U.S. Pat. No. 4,498,387 issued Feb. 12, 1985; Talbott, U.S. Pat. No. 4,129,206 issued Dec. 12, 1978; Urban et al., U.S. Pat. No. 4,018,151 issued Apr. 19, 1977; Zurick, U.S. Pat. No. 3,356,019 issued Dec. 5, 1967; Zurick, U.S. Pat. No. 3,491,686 issued Jan. 27, 1970; and Zurick, U.S. Pat. No. 3,521,554 issued July 21, 1970.
A problem with prior art skip-print systems has been that the trip mechanism for the skip-print system must be actuated prior to the time that a mandrel is in the immediate vicinity of the blanket wheel in order for the skip-print system to have sufficient time to move the mandrel from its ordinary, blanket wheel contacting path to a path which is spaced apart from the blanket wheel. In such a system, the detection device which senses the absence of a can or an improperly seated can on a mandrel is necessarily positioned a substantial distance "upstream" of the blanket wheel contact area. As a result of this upstream positioning, such a detection device cannot sense a can which becomes unseated from a mandrel at a point downstream of the detection device but upstream of the blanket wheel contact area. In extremely high speed machines, this problem is accentuated because the detection device senses a can/mandrel seating arrangement prior to the time that the can seating (transfer of the can body from a pocket opposite a mandrel to the mandrel) is completed. Thus, a seating detection device is required to predict whether or not a given can will seat on a mandrel, rather than actually observing the proper seating or lack of proper seating. Since such "predictions" are necessarily less accurate than an observation of the can/mandrel seating arrangement immediately prior to contact of the can with the blanket wheel, misseated cans are occasionally printed. Such printing results in an improper image transfer to the can (known in the trade as "partial litho") as well as contamination of the associated mandrel with printing medium.
Another problem with prior art systems has been that the skip-print mechanical assembly for various reasons may not respond to a skip-print command signal from the detection device. Thus, even if the detection device properly senses a misseated can or the absence of a can, the skip-print system may malfunction due to a problem in the skip-print mechanical assembly or due to a problem in the signal transfer between the detection device and the skip-print mechanical assembly.
The printing of a mandrel having a misseated can or no can thereon is thus possible even if the mandrel wheel assembly is provided with a skip-print system. In view of this fact, it would be generally desirable to provide a system for monitoring the operation of the skip-print system and for detecting system malfunctions that will result in the printing of a mandrel. It would be further desirable to provide a system which takes appropriate corrective action in response to such a skip-print system malfunction so as to: (1) reject partially printed cans; (2) reject cans with ink on interior surfaces thereof caused by contact with a printed mandrel; and (3) clean any mandrel that has been printed.